21668840 has 16 divisors (see below), whose sum is σ = 48754980. Its totient is φ = 8667520.

The previous prime is 21668839. The next prime is 21668851. The reversal of 21668840 is 4886612.

It can be written as a sum of positive squares in 2 ways, for example, as 19589476 + 2079364 = 4426^2 + 1442^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21668840.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 270821 + ... + 270900.

Almost surely, 2^21668840 is an apocalyptic number.

21668840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21668840 is an abundant number, since it is smaller than the sum of its proper divisors (27086140).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21668840 is a wasteful number, since it uses less digits than its factorization.

21668840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 541732 (or 541728 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 35.

The square root of 21668840 is about 4654.9801288512. The cubic root of 21668840 is about 278.7908745788.

The spelling of 21668840 in words is "twenty-one million, six hundred sixty-eight thousand, eight hundred forty".